'Research into Climate Change Must Be Accurate and Our Reactions Must Be Balanced'
Rees, Sir Martin, The Independent (London, England)
The stakes are too high to allow controversy and dogma to cloud our views of climate science, writes Sir Martin Rees
There's no denying where science has recently had the most contentious policy impact: climate change. The stakes are high, because climate change could seriously impact on the lives of future generations, and irreversibly modify our ecosystem.
The political challenge is daunting. The global scale of the problem necessitates international action; the actions required to mitigate and reduce the impacts may be costly (although the costs of inaction are projected by many to be greater); and the most serious impacts lie decades in the future - and in politics the urgent tends to trump the long term. Climate science has a central role to play in informing these policy decisions, and those making the decisions must have access to climate science of the highest quality.
The best scientific information available provides strong evidence that the warming of the earth over the past half-century has been caused largely by human activity, such as the burning of fossil fuels and changes in land use, including agriculture and deforestation.
But what about the future trends? There is, in my view, one decisive line of evidence which in itself justifies the prominence of climate change on the agenda: there is more carbon dioxide (CO2) in the atmosphere than there has been for at least the past 500,000 years, mainly because of the burning of fossil fuels.
This measurement isn't controversial. Moreover, straightforward projections of global power consumption suggest that, if we continue to depend on fossil fuels to the extent we do today, the CO2 concentration would more than double in the next 50 years.
And straightforward chemistry, known since the 19th century, tells us that CO2 is a "greenhouse gas": it acts like a blanket, preventing some of the heat radiated by the earth from escaping freely into space. So the build-up of CO2 in the atmosphere will trigger a long-term warming, superimposed on all the other complicated effects that under natural conditions cause the climate to fluctuate.
The actual sensitivity of the climate to the CO2 concentration is, however, uncertain. This is because some key "feedback" processes are poorly understood.
Any warming trend will change the amount of water vapour in the atmosphere, and the cloud cover; and these changes will themselves affect the blanketing. The best calculations indicate that a doubling of the CO2 concentration would lead to a rise in the global mean temperature somewhere between C and 4.5C.
The mean temperature rise is, however, just the "headline message". It's important to realise that the warming won't be uniform: climatic patterns will shift.
Temperatures will rise fastest on land, particularly on the northern continents in winter. A 4C mean global rise could lead to a warming of 10C in some places.
However, climate models are not yet refined enough to predict with confidence the local impacts - for example, changes in the monsoons, or in drought patterns in Africa - that could be most crucial for policy. Moreover, the greater the warming, the greater the risk of triggering processes - such as the melting of Greenland's ice cap, with consequent sea level rises, or methane release from the tundra, which would lead to a stronger greenhouse effect and further warming.
Despite the threat posed by the cumulative build-up of CO2 in the atmosphere, annual CO2 emissions continue to rise. Many hoped that agreement would be reached at the 2009 Copenhagen meeting to halve global CO2 emissions by 2050. This would have corresponded to a "ration" of two tons of CO2 per year for each person on the planet.
By way of comparison, the current US and Australian level is 20, the European figure is about 10, the Chinese level is already 5. …